1. Field of the Invention
This invention is generally related to corrosion control systems and is specifically directed to a corrosion control apparatus and method for protecting hard to reach crevices, openings and voids such as in pipe flanges.
2. Description of the Prior Art
Poorly coated pipe flanges in corrosive environment are the leading cause of premature paint failure on process pipe and surrounding platforms. Many crevices and annular spaces exist in the body of a flange and sealing faces. These areas are difficult to coat. Inevitable damage to the coating system of the flange occurs when it is assembled. Once in service, it is impossible to coat the inner spaces of flange. What results is exposed steel, free to corrode in the atmosphere. Any ingress of water into the flange makes bare steel corrode. Water from rain, offshore storms, washdown, drilling or any other cause, accelerates the corrosion. Draining water then pushes the corrosive substances out of the flange gaps to drip onto adjacent painted surfaces.
The problem is further exacerbated on older flanges having corrosion already inside. Indeed, when existing flanges are painted, it is not uncommon to find residual blasting sand or grit lodged between the fasteners and the flange body, or inside the bolt hole annuli. This grit acts like a sponge to retain water inside the flange and promote rapid failure of the applied paint system. Flange corrosion maybe visible after three to six months after the flange has been painted.
For many industries, the cost of painting process piping represents a major percentage of the corrosion control budget. Since the earliest signs of paint failure typically occur on the small diameter piping and fitting, they are painted more frequently than the structural area. Therefore, the cost per square foot to paint flanges is often as much as three and one half times greater than structural areas.
Crevice corrosion at the gasket to flange interface with its associated progressive failure of neighboring painted surfaces is a problem industries have long recognized. Since corrosion failure often stems from poorly coated flanges, many different methods and devices have been developed in an attempt to seal the flange, each having its own failings.
Flange protectors are the most expensive approach to corrosion control and have many problems associated with their use. A crevice is formed when the band is attached to the flange. The crevice accelerates the coating failure on the outside of the flange. Ultimately the corrosion substances under the band will swell and cause deformation of the band and even possible breakage. To be effective, periodic maintenance is required to check and refill the inhibited grease injected into the annular confines. However, this is impractical for many applications. Furthermore, corrosion maybe ongoing under a deformed protector and there is no way to see it.
Caulking compounds of various types have also been used to fight corrosion. These compounds are unsuccessful for many reasons. Caulk does not bond to steel. Thus, a tight crevice is formed, retaining water through capillary action. Further, once the initial seal is violated, remaining caulk actually retains water by preventing natural evaporation.
Another method of preventing corrosion includes temporarily sealing the flange by filling it with a wax material. This approach is expensive and does not allow for inspection of the flange. As an alternative, a flange may be flooded with conventional paint. However, because paints do not establish a bond with corroded steel, there is no long term protection.
Although there have been various attempts to fill and tape flange connections, the prior art methods are labor intensive, increasing the cost of installations. Often the sealing material does not displace all the water and does not wet the steel. Anaerobic conditions result, with an associated microbial induced corrosion risk. Taping alone is not a good idea as it has a limited life and upon failure, the problem is free to continue. In addition, many substances used as the fill contain pollutants and are environmental unsafe.
A need exists therefore for a cost effective method of controlling corrosion of pipe flanges that is easy to apply, capable of being inspected, displaces residual moisture, requires no maintenance, is environmentally safe and will endure the life of the paint system.